This invention relates to catalytic free radical polymerization of vinyl monomers in a suspension or emulsion system.
It is well known in the art that vinyl organic compounds can be polymerized to form higher molecular weight compounds. It is also known that these vinyl compounds (monomers) undergo free radical polymerization more readily with certain catalysts, particularly oxidizing catalysts, such as peroxides and persulfates. These monomers upon standing undergo some autopolymerization, and high temperatures promote such polymerization. Since the monomers are often produced at one locality and the polymerization takes place at a different locality, often stabilizers are added to the monomer to insure that no polymerization will take place prior to the desired controlled polymerization to be carried out at the proper time under controlled conditions. Many of the known polymerization catalysts, such as persulfate salts, aziosobutyronitrile, benzoyl peroxide, and the like, are thermally unstable and present fire and/or explosion hazards. The stabilizers used with monomers consume conventional catalysts or initiators so that an excess of catalyst than that required for pure monomers must be used.
It is also known that different monomers can be copolymerized. Polymerization can be effected in vapor phase; however, most commercial polymerizations are carried out with the monomer suspended in an inert liquid or emulsion, generally in water. It is also well known that monomers used and concentration, temperature, catalyst, promoter, plasticizer, and the like, will affect the properties of the polymer formed. Depending upon the polymer, these materials are useful for molding, casting, film forming, and foaming into a multitude of products.
In suspension or emulsion polymerization, temperatures and pressures are chosen to optimize the production of a polymer of the desired characteristics, utilizing the particular catalyst. It is obvious that the temperature used must be below the vaporization temperature of any of the components of the system including the carrier liquid. With conventional catalysts, polymerization rates increase with temperature; but, at the same time, lower molecular weights of polymer are obtained at the higher temperatures. Therefore, catalysts and promoters are utilized to promote polymerization at relatively lower temperatures.